1. Field of the Invention
The present invention relates to a manufacturing method of a supporting structure for vehicle. More particularly, the present invention relates to a manufacturing method of a supporting structure for vehicle characterized in that the supporting structure itself is plastically deformed when a load not less than a setting load is given to the supporting structure so that an impact force impressed upon the supporting structure can be relaxed.
2. Description of Related Art
In a supporting structure for supporting and fixing an engine, transmission, differential gear and so forth, a mechanism is provided which absorbs and relaxes impact energy by the plastic deformation of the supporting structure itself when a load not less than a predetermined value is given by a collision to an object to be supported such as an engine attached to the supporting structure.
For example, Japanese Patent Unexamined Publication JP-A-2002-2310 discloses a bracket used for supporting a power plant which includes a flange portion, on the side of which a notch groove having a V-shaped cross section is formed, and when a load not less than a predetermined value is given, the flange portion is broken from a starting point of the notch groove so that an impact force given to the bracket can be relaxed.
Japanese Patent Unexamined Publication JP-A-2002-127762 discloses an engine mount having a notch portion which becomes a starting point of the plastic deformation or destruction when a load not less than a predetermined value is given to the engine supporting structure.
A supporting structure, which absorbs and relaxes impact energy by the plastic deformation of the supporting structure when a load not less than a predetermined value is given to an object to be supported such as an engine, transmission and differential gear, is formed into various shapes according to a type of the object to be supported and an attaching position. Further, the proof stress, at which the plastic deformation of the supporting structure is made, is variously changed. Concerning the method of forming such various supporting structures and portions which allow the supporting structures to be plastically deformed, when machining such as cutting is employed, the machining work becomes complicated and the manufacturing cost is raised.